The　seismic　fragility　of　the　transfer　and　purging　chamber　in　a　nuclear　power　plant　is　assessed　in　this　paper　based　on　the　incremental　dynamic　analysis　method.　Select　the　peak　ground　acceleration　as　the　ground　motion　intensity　measure,　and　select　the　compressive　strain　of　concrete,　steel　plate　stress,　and　peak　displacement　of　the　structure　as　the　damage　measures.　This　paper　calculates　the　dynamic　response　of　the　transfer　and　purging　chamber　under　160　seismic　conditions　and　analyzes　the　conditional　failure　probabilities　of　no　damage,　slight　damage,　recoverable　damage,　and　serious　damage.　The　result　shows　that　the　conditional　failure　probabilities　of　concrete　and　steel　plate　have　remarkable　differences　under　the　design　basis　ground　motions,　and　both　are　lower　than　the　criterion　restriction.　The　conditional　failure　probability　of　peak　displacement　of　the　cantilever　in　the　transfer　and　purging　chamber　under　the　design　basis　ground　motions　exceeds　the　criterion　restriction.　It　indicates　that　peak　displacement　of　the　cantilever　is　overlarge　in　one　direction　caused　by　insufficient　constraints　and　too　small　local　stiffness.　The　failure　probability　of　the　transfer　and　purging　chamber　that　does　not　meet　operational　basis　performance　demand　is　6.32　x　10(-2)parts　per　thousand,　and　the　failure　probability　of　the　transfer　and　purging　chamber　that　does　not　meet　safety　shutdown　performance　demand　is　1.76　x　10(-3)parts　per　thousand.